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Type II supernova sub-categories are classified based on their light curves, which describe how the intensity of the light changes over time. The light of Type II-L supernovas declines steadily after the explosion, while the light of Type II-P supernovas stays steady for a longer period before diminishing. Both types have the signature of hydrogen in their spectra. The quadruple star HD 74438, belonging to the open cluster IC 2391 the Vela constellation, has been predicted to become a non-standard type Ia supernova. [98] [99] Core collapse [ edit ] The layers of a massive, evolved star just before core collapse (not to scale) Exactly how a star dies depends in part on its mass. Our sun, for example, doesn't have enough mass to explode as a supernova. (Though the news for Earth still isn't good, because once the sun runs out of its nuclear fuel, perhaps in a couple billion years, it will swell into a red giant that will likely vaporize our world, before gradually cooling into a white dwarf.) But with the right amount of mass, a star can burn out in a fiery explosion. Types of supernovas The real anticipation now is that we’ll have the trifecta—electromagnetic waves, gravitational waves and neutrinos—from a supernova explosion,” says Ray Jayawardhana, an astronomer at Cornell University. “That would be an incredibly rich source of information and insights.”

Main article: Type Ib and Ic supernovae Type Ib SN 2008D [120] at the far upper end of the galaxy, shown in X-ray (left) and visible light (right), [121] with the brighter SN 2007uy closer to the centre The last supernova directly observed in the Milky Way was Kepler's Supernova in 1604, appearing not long after Tycho's Supernova in 1572, both of which were visible to the naked eye. The remnants of more recent supernovae have been found, and observations of supernovae in other galaxies suggest they occur in the Milky Way on average about three times every century. A supernova in the Milky Way would almost certainly be observable through modern astronomical telescopes. The most recent naked-eye supernova was SN 1987A, which was the explosion of a blue supergiant star in the Large Magellanic Cloud, a satellite of the Milky Way. A supernovaonly burns for a small while, yeteach one lets out an incredible amount of information regarding our universe. Because supernovae are relatively rare events within a galaxy, occurring about three times a century in the Milky Way, [40] obtaining a good sample of supernovae to study requires regular monitoring of many galaxies. Today, amateur and professional astronomers are finding several hundred every year, some when near maximum brightness, others on old astronomical photographs or plates. Supernovae in other galaxies cannot be predicted with any meaningful accuracy. Normally, when they are discovered, they are already in progress. [41] To use supernovae as standard candles for measuring distance, observation of their peak luminosity is required. It is therefore important to discover them well before they reach their maximum. Amateur astronomers, who greatly outnumber professional astronomers, have played an important role in finding supernovae, typically by looking at some of the closer galaxies through an optical telescope and comparing them to earlier photographs. [42] In the re-ignition of a white dwarf, the object's temperature is raised enough to trigger runaway nuclear fusion, completely disrupting the star. Possible causes are an accumulation of material from a binary companion through accretion, or by a stellar merger.The model for the formation of this category of supernova is a close binary star system. The larger of the two stars is the first to evolve off the main sequence, and it expands to form a red giant. The two stars now share a common envelope, causing their mutual orbit to shrink. The giant star then sheds most of its envelope, losing mass until it can no longer continue nuclear fusion. At this point, it becomes a white dwarf star, composed primarily of carbon and oxygen. [84] Eventually, the secondary star also evolves off the main sequence to form a red giant. Matter from the giant is accreted by the white dwarf, causing the latter to increase in mass. The exact details of initiation and of the heavy elements produced in the catastrophic event remain unclear. [85]

There are several means by which a supernova of this type can form, but they share a common underlying mechanism. If a carbon- oxygen white dwarf accreted enough matter to reach the Chandrasekhar limit of about 1.44 solar masses [77] (for a non-rotating star), it would no longer be able to support the bulk of its mass through electron degeneracy pressure [78] [79] and would begin to collapse. However, the current view is that this limit is not normally attained; increasing temperature and density inside the core ignite carbon fusion as the star approaches the limit (to within about 1%) [80] before collapse is initiated. [77] In contrast, for a core primarily composed of oxygen, neon and magnesium, the collapsing white dwarf will typically form a neutron star. In this case, only a fraction of the star's mass will be ejected during the collapse. [79] The blue spot at the centre of the red ring is an isolated neutron star in the Small Magellanic Cloud. So the resultant light from this explosion has been traveling through space for 21 million years before it finally reached our planet last week. One specific type of supernova originates from exploding white dwarfs, like type Ia, but contains hydrogen lines in their spectra, possibly because the white dwarf is surrounded by an envelope of hydrogen-rich circumstellar material. These supernovae have been dubbed type Ia/IIn, type Ian, type IIa and type IIan. [97] Today’s astronomers are much better prepared for the next supernova than Kepler would have been—or than anyone would have been just a few decades ago. Today’s scientists are equipped with telescopes that record visible light. These instruments will show what a supernova would look like if we could fly close to it and look at it with our own eyes. But we also have telescopes that can record infrared light—light whose colors lie beyond the red end of the visible spectrum. With its longer wavelengths, infrared light can pass more easily through gas and dust than visible light, revealing targets that may be impossible to see with traditional telescopes. The James Webb Space Telescope, for example, records primarily in the infrared. Both visible and infrared light are part of the “electromagnetic spectrum,” but supernovas also emit a different kind of radiation, in the form of subatomic particles called neutrinos—and today we have detectors to snare them, too. As well, astronomers now have detectors that can record subtle ripples in the fabric of spacetime known as gravitational waves, which are also believed to be unleashed by exploding stars. Could a nearby supernova pose a threat to life on Earth? Yes, in theory—but the blast would have to be very close, and at the moment no such nearby stars are at risk of exploding. Which is a good thing, because the blast of radiation from a nearby supernova would be devastating. Over a period of weeks, the supernova would emit ultraviolet rays, X-rays and gamma rays, which wouldn’t necessarily reach the ground, but would still wreak havoc on the Earth’s protective ozone layer, explains Fields. “So it wouldn’t turn us into the Hulk—but it would strip the ozone layer off the stratosphere,” he says. Without the ozone layer, the Earth would be awash in deadly ultraviolet radiation from the sun; this could wipe out phytoplankton in the oceans, with the effects working their way up the food chain, possibly leading to a mass extinction, Fields says.For other uses, see Supernova (disambiguation). SN 1994D (bright spot on the lower left), a type Ia supernova within its host galaxy, NGC 4526 Scientists have described two distinct types of supernovas. In a Type I supernova, a white dwarf star pulls material off a companion star until a runaway nuclear reaction ignites; the white dwarf is blown apart, sending debris hurtling through space. Kepler’s was a Type I. In a Type II supernova, sometimes called a core-collapse supernova, a star exhausts its nuclear fuel supply and collapses under its own gravity; the collapse then “bounces,” triggering an explosion. Abnormally bright type Ia supernovae occur when the white dwarf already has a mass higher than the Chandrasekhar limit, [91] possibly enhanced further by asymmetry, [92] but the ejected material will have less than normal kinetic energy. This super-Chandrasekhar-mass scenario can occur, for example, when the extra mass is supported by differential rotation. [93] A supernova occurs when there is a change in the core of a star, one much bigger than our sun. These changes can occur in two different ways, both of which result in a supernova. A second model for the formation of type Ia supernovae involves the merger of two white dwarf stars, with the combined mass momentarily exceeding the Chandrasekhar limit. [88] This is sometimes referred to as the double-degenerate model, as both stars are degenerate white dwarfs. Due to the possible combinations of mass and chemical composition of the pair there is much variation in this type of event, [89] and, in many cases, there may be no supernova at all, in which case they will have a less luminous light curve than the more normal SN type Ia. [90] Non-standard Type Ia [ edit ]

A later video appeared to show Argamani being held captive in a room with a tiled floor, sipping from a bottle of water. In a Type Ia supernova, the supernova process happens when the white dwarf in the binary accretes too much mass (anything over about 1.44 times the mass of our sun). The exact cause of the explosion is still an active area of research, but many think that the extra mass makes the core of the white dwarf heat up, which leads to too much pressure and energy inside the star that it is no longer able to support, and the star violently explodes. A few supernovae, such as SN 1987K [69] and SN 1993J, appear to change types: they show lines of hydrogen at early times, but, over a period of weeks to months, become dominated by lines of helium. The term "type IIb" is used to describe the combination of features normally associated with types II and Ib. [61] A knot in the central ring of Supernova 1987A, as observed by the Hubble Space Telescope in 1994 (left) and 1997 (right).The knot is caused by the collision of the supernova's blast wave with a slower-moving ring of matter it had ejected earlier. The bright spot on the lower left is an unrelated star. (more) Louk’s mother, Ricarda, later said: “This morning my daughter, Shani Nicole Louk, a German citizen, was kidnapped with a group of tourists in southern Israel by Palestinian Hamas.Astronomers classify supernovae according to their light curves and the absorption lines of different chemical elements that appear in their spectra. If a supernova's spectrum contains lines of hydrogen (known as the Balmer series in the visual portion of the spectrum) it is classified Type II; otherwise it is Type I. In each of these two types there are subdivisions according to the presence of lines from other elements or the shape of the light curve (a graph of the supernova's apparent magnitude as a function of time). [60] [61] Supernova taxonomy [60] [61] Type I Type I supernova: A star accumulates matter from a nearby neighbor until a runaway nuclear reaction ignites. As survey programmes rapidly increase the number of detected supernovae, collated collections of observations (light decay curves, astrometry, pre-supernova observations, spectroscopy) have been assembled. The Pantheon data set, assembled in 2018, detailed 1048 supernovae. [52] In 2021, this data set was expanded to 1701 light curves for 1550 supernovae taken from 18 different surveys, a 50% increase in under 3 years. [53] Naming convention [ edit ] Multi-wavelength X-ray, infrared, and optical compilation image of Kepler's supernova remnant, SN 1604 The closest and most easily observed of the hundreds of supernovae that have been recorded since 1604 was first sighted on the morning of Feb. 24, 1987, by the Canadian astronomer Ian K. Shelton while working at the Las Campanas Observatory in Chile. Designated SN 1987A, this formerly extremely faint object attained a magnitude of 4.5 within just a few hours, thus becoming visible to the unaided eye. The newly appearing supernova was located in the Large Magellanic Cloud at a distance of about 160,000 light-years. It immediately became the subject of intense observation by astronomers throughout the Southern Hemisphere and was observed by the Hubble Space Telescope. SN 1987A’s brightness peaked in May 1987, with a magnitude of about 2.9, and slowly declined in the following months. Types of supernovae The table below lists the known reasons for core collapse in massive stars, the types of stars in which they occur, their associated supernova type, and the remnant produced. The metallicity is the proportion of elements other than hydrogen or helium, as compared to the Sun. The initial mass is the mass of the star prior to the supernova event, given in multiples of the Sun's mass, although the mass at the time of the supernova may be much lower. [100]